////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2018-2021 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Octave is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
//
////////////////////////////////////////////////////////////////////////

#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include <QAction>
#include <QApplication>
#include <QCompleter>
#include <QDesktopServices>
#include <QDir>
#include <QFile>
#include <QFileInfo>
#include <QHelpContentWidget>
#include <QHelpIndexWidget>
#if defined (HAVE_NEW_QHELPINDEXWIDGET_API) \
  || defined (HAVE_QHELPENGINE_DOCUMENTSFORIDENTIFIER)
#  include <QHelpLink>
#endif
#include <QHelpSearchEngine>
#include <QHelpSearchQueryWidget>
#include <QHelpSearchResultWidget>
#include <QLabel>
#include <QLineEdit>
#include <QMessageBox>
#include <QTabWidget>
#include <QTimer>
#include <QVBoxLayout>

#include "documentation.h"
#include "documentation-bookmarks.h"
#include "gui-preferences-global.h"
#include "gui-preferences-dc.h"
#include "gui-preferences-sc.h"
#include "octave-qobject.h"
#include "shortcut-manager.h"

#include "defaults.h"
#include "file-ops.h"
#include "oct-env.h"

namespace octave
{
  // The documentation splitter, which is the main widget
  // of the doc dock widget
  documentation::documentation (QWidget *p, base_qobject& oct_qobj)
    : QSplitter (Qt::Horizontal, p),
      m_octave_qobj (oct_qobj), m_doc_widget (this),
      m_tool_bar (new QToolBar (this)),
      m_query_string (QString ()),
      m_indexed (false),
      m_current_ref_name (QString ()),
      m_prev_pages_menu (new QMenu (this)),
      m_next_pages_menu (new QMenu (this)),
      m_prev_pages_count (0),
      m_next_pages_count (0),
      m_findnext_shortcut (new QShortcut (this)),
      m_findprev_shortcut (new QShortcut (this))
  {
    // Get original collection
    QString collection = getenv ("OCTAVE_QTHELP_COLLECTION");
    if (collection.isEmpty ())
      collection = QString::fromStdString (config::oct_doc_dir ()
                                           + sys::file_ops::dir_sep_str ()
                                           + "octave_interpreter.qhc");

    // Setup the help engine with the original collection, use a writable copy
    // of the original collection and load the help data
    m_help_engine = new QHelpEngine (collection, this);

    // Mark help as readonly to avoid error if collection file is stored in a
    // readonly location
    m_help_engine->setProperty ("_q_readonly",
                                QVariant::fromValue<bool> (true));

    QString tmpdir = QDir::tempPath();
    m_collection
      = QString::fromStdString (sys::tempnam (tmpdir.toStdString (),
                                              "oct-qhelp-"));

    if (m_help_engine->copyCollectionFile (m_collection))
      m_help_engine->setCollectionFile (m_collection);
    else
#ifdef ENABLE_DOCS
      // FIXME: Perhaps a better way to do this would be to keep a count
      // in the GUI preferences file.  After issuing this warning 3 times
      // it would be disabled.  The count would need to be reset when a new
      // version of Octave is installed.
      QMessageBox::warning (this, tr ("Octave Documentation"),
                            tr ("Could not copy help collection to temporary\n"
                                "file. Search capabilities may be affected.\n"
                                "%1").arg (m_help_engine->error ()));
#endif

    connect(m_help_engine->searchEngine (), SIGNAL(indexingFinished ()),
            this, SLOT(load_index ()));
    connect(m_help_engine, SIGNAL(setupFinished ()),
            m_help_engine->searchEngine (), SLOT(reindexDocumentation ()));

    if (! m_help_engine->setupData())
      {
#ifdef ENABLE_DOCS
        QMessageBox::warning (this, tr ("Octave Documentation"),
                              tr ("Could not setup the data required for the\n"
                                  "documentation viewer. Only help texts in\n"
                                  "the Command Window will be available."));
#endif

        disconnect (m_help_engine, 0, 0, 0);

        delete m_help_engine;
        m_help_engine = nullptr;
      }

    // The browser
    QWidget *browser_find = new QWidget (this);
    m_doc_browser = new documentation_browser (m_help_engine, browser_find);
    connect (m_doc_browser, &documentation_browser::cursorPositionChanged,
             this, &documentation::handle_cursor_position_change);

    // Tool bar
    construct_tool_bar ();

    // Find bar
    QWidget *find_footer = new QWidget (browser_find);
    QLabel *find_label = new QLabel (tr ("Find:"), find_footer);
    m_find_line_edit = new QLineEdit (find_footer);
    connect (m_find_line_edit, &QLineEdit::returnPressed,
             this, [=] () { find (); });
    connect (m_find_line_edit, &QLineEdit::textEdited,
             this, &documentation::find_forward_from_anchor);
    QToolButton *forward_button = new QToolButton (find_footer);
    forward_button->setText (tr ("Search forward"));
    forward_button->setToolTip (tr ("Search forward"));
    resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
    forward_button->setIcon (rmgr.icon ("go-down"));
    connect (forward_button, &QToolButton::pressed,
             this, [=] () { find (); });
    QToolButton *backward_button = new QToolButton (find_footer);
    backward_button->setText (tr ("Search backward"));
    backward_button->setToolTip (tr ("Search backward"));
    backward_button->setIcon (rmgr.icon ("go-up"));
    connect (backward_button, &QToolButton::pressed,
             this, &documentation::find_backward);
    QHBoxLayout *h_box_find_footer = new QHBoxLayout (find_footer);
    h_box_find_footer->addWidget (find_label);
    h_box_find_footer->addWidget (m_find_line_edit);
    h_box_find_footer->addWidget (forward_button);
    h_box_find_footer->addWidget (backward_button);
    h_box_find_footer->setMargin (2);
    find_footer->setLayout (h_box_find_footer);

    QVBoxLayout *v_box_browser_find = new QVBoxLayout (browser_find);
    v_box_browser_find->addWidget (m_tool_bar);
    v_box_browser_find->addWidget (m_doc_browser);
    v_box_browser_find->addWidget (find_footer);
    browser_find->setLayout (v_box_browser_find);

    notice_settings (rmgr.get_settings ());

    m_findnext_shortcut->setContext (Qt::WidgetWithChildrenShortcut);
    connect (m_findnext_shortcut, &QShortcut::activated,
             this, [=] () { find (); });
    m_findprev_shortcut->setContext (Qt::WidgetWithChildrenShortcut);
    connect (m_findprev_shortcut, &QShortcut::activated,
             this, &documentation::find_backward);

    find_footer->hide ();
    m_search_anchor_position = 0;

    if (m_help_engine)
      {
#if defined (HAVE_NEW_QHELPINDEXWIDGET_API)
        // Starting in Qt 5.15, help engine uses filters instead of old API
        m_help_engine->setUsesFilterEngine (true);
#endif
        // Layout contents, index and search
        QTabWidget *navi = new QTabWidget (this);
        navi->setTabsClosable (false);
        navi->setMovable (true);

        // Contents
        QHelpContentWidget *content = m_help_engine->contentWidget ();
        content->setObjectName ("documentation_tab_contents");
        navi->addTab (content, tr ("Contents"));

        connect (m_help_engine->contentWidget (),
                 &QHelpContentWidget::linkActivated,
                 m_doc_browser, [=] (const QUrl& url) {
                   m_doc_browser->handle_index_clicked (url); });

        // Index
        QHelpIndexWidget *index = m_help_engine->indexWidget ();

        m_filter = new QComboBox (this);
        m_filter->setToolTip (tr ("Enter text to search the indices"));
        m_filter->setEditable (true);
        m_filter->setInsertPolicy (QComboBox::NoInsert);
        m_filter->setMaxCount (10);
        m_filter->setMaxVisibleItems (10);
        m_filter->setSizeAdjustPolicy (QComboBox::AdjustToMinimumContentsLengthWithIcon);
        QSizePolicy sizePol (QSizePolicy::Expanding, QSizePolicy::Preferred);
        m_filter->setSizePolicy (sizePol);
        m_filter->completer ()->setCaseSensitivity (Qt::CaseSensitive);
        QLabel *filter_label = new QLabel (tr ("Search"));

        QWidget *filter_all = new QWidget (navi);
        QHBoxLayout *h_box_index = new QHBoxLayout (filter_all);
        h_box_index->addWidget (filter_label);
        h_box_index->addWidget (m_filter);
        h_box_index->setMargin (2);
        filter_all->setLayout (h_box_index);

        QWidget *index_all = new QWidget (navi);
        index_all->setObjectName ("documentation_tab_index");
        QVBoxLayout *v_box_index = new QVBoxLayout (index_all);
        v_box_index->addWidget (filter_all);
        v_box_index->addWidget (index);
        index_all->setLayout (v_box_index);

        navi->addTab (index_all, tr ("Function Index"));

#if defined (HAVE_NEW_QHELPINDEXWIDGET_API)
        connect (m_help_engine->indexWidget (),
                 &QHelpIndexWidget::documentActivated,
                 this, [=] (const QHelpLink &link) {
                   m_doc_browser->handle_index_clicked (link.url); });
#else
        connect (m_help_engine->indexWidget (),
                 &QHelpIndexWidget::linkActivated,
                 m_doc_browser, &documentation_browser::handle_index_clicked);
#endif

        connect (m_filter, &QComboBox::editTextChanged,
                 this, &documentation::filter_update);

        connect (m_filter->lineEdit (), &QLineEdit::editingFinished,
                 this, &documentation::filter_update_history);

        // Bookmarks (own class)
        m_bookmarks
          = new documentation_bookmarks (this, m_doc_browser, m_octave_qobj, navi);
        navi->addTab (m_bookmarks, tr ("Bookmarks"));

        connect (m_action_bookmark, &QAction::triggered,
                 m_bookmarks, [=] () { m_bookmarks->add_bookmark (); });

        // Search
        QHelpSearchEngine *search_engine = m_help_engine->searchEngine ();
        QHelpSearchQueryWidget *search = search_engine->queryWidget ();
        QHelpSearchResultWidget *result = search_engine->resultWidget ();
        QWidget *search_all = new QWidget (navi);
        QVBoxLayout *v_box_search = new QVBoxLayout (search_all);
        v_box_search->addWidget (search);
        v_box_search->addWidget (result);
        search_all->setLayout (v_box_search);
        search_all->setObjectName ("documentation_tab_search");
        navi->addTab (search_all, tr ("Search"));

        connect (search, &QHelpSearchQueryWidget::search,
                 this, &documentation::global_search);

        connect (search_engine, &QHelpSearchEngine::searchingStarted,
                 this, &documentation::global_search_started);
        connect (search_engine, &QHelpSearchEngine::searchingFinished,
                 this, &documentation::global_search_finished);

        connect (search_engine->resultWidget (),
                 &QHelpSearchResultWidget::requestShowLink,
                 this, &documentation::handle_search_result_clicked);

        // Fill the splitter
        insertWidget (0, navi);
        insertWidget (1, browser_find);
        setStretchFactor (1, 1);
      }
  }

  documentation::~documentation (void)
  {
    // Cleanup temporary file and directory
    QFile file (m_collection);
    if (file.exists ())
      {
        QFileInfo finfo (file);
        QString bname = finfo.fileName ();
        QDir dir = finfo.absoluteDir ();
        dir.setFilter (QDir::Dirs | QDir::NoDotAndDotDot | QDir::Hidden);
        QStringList namefilter;
        namefilter.append ("*" + bname + "*");
        for (const auto& fi : dir.entryInfoList (namefilter))
          {
            std::string file_name = fi.absoluteFilePath ().toStdString ();
            sys::recursive_rmdir (file_name);
          }

        file.remove();
      }
  }

  QAction * documentation::add_action (const QIcon& icon, const QString& text,
                                       const char *member, QWidget *receiver,
                                       QToolBar *tool_bar)
  {
    QAction *a;
    QWidget *r = this;
    if (receiver != nullptr)
      r = receiver;

    a = new QAction (icon, text, this);

    if (member)
      connect (a, SIGNAL (triggered ()), r, member);

    if (tool_bar)
      tool_bar->addAction (a);

    m_doc_widget->addAction (a);  // important for shortcut context
    a->setShortcutContext (Qt::WidgetWithChildrenShortcut);

    return a;
  }

  void documentation::construct_tool_bar (void)
  {
    // Home, Previous, Next
    resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
    m_action_go_home
      = add_action (rmgr.icon ("go-home"), tr ("Go home"), SLOT (home (void)),
                    m_doc_browser, m_tool_bar);

    m_action_go_prev
      = add_action (rmgr.icon ("go-previous"), tr ("Go back"),
                    SLOT (backward (void)), m_doc_browser, m_tool_bar);
    m_action_go_prev->setEnabled (false);

    // popdown menu with prev pages files
    QToolButton *popdown_button_prev_pages = new QToolButton ();
    popdown_button_prev_pages->setToolTip (tr ("Previous pages"));
    popdown_button_prev_pages->setMenu (m_prev_pages_menu);
    popdown_button_prev_pages->setPopupMode (QToolButton::InstantPopup);
    popdown_button_prev_pages->setToolButtonStyle (Qt::ToolButtonTextOnly);
    popdown_button_prev_pages->setCheckable (false);
    popdown_button_prev_pages->setArrowType(Qt::DownArrow);
    m_tool_bar->addWidget (popdown_button_prev_pages);

    m_action_go_next
      = add_action (rmgr.icon ("go-next"), tr ("Go forward"),
                    SLOT (forward (void)), m_doc_browser, m_tool_bar);
    m_action_go_next->setEnabled (false);

    // popdown menu with prev pages files
    QToolButton *popdown_button_next_pages = new QToolButton ();
    popdown_button_next_pages->setToolTip (tr ("Next pages"));
    popdown_button_next_pages->setMenu (m_next_pages_menu);
    popdown_button_next_pages->setPopupMode (QToolButton::InstantPopup);
    popdown_button_next_pages->setToolButtonStyle (Qt::ToolButtonTextOnly);
    popdown_button_next_pages->setArrowType(Qt::DownArrow);
    m_tool_bar->addWidget (popdown_button_next_pages);

    connect (m_doc_browser, &documentation_browser::backwardAvailable,
             m_action_go_prev, &QAction::setEnabled);
    connect (m_doc_browser, &documentation_browser::backwardAvailable,
             popdown_button_prev_pages, &QToolButton::setEnabled);
    connect (m_doc_browser, &documentation_browser::forwardAvailable,
             m_action_go_next, &QAction::setEnabled);
    connect (m_doc_browser, &documentation_browser::forwardAvailable,
             popdown_button_next_pages, &QToolButton::setEnabled);
    connect (m_doc_browser, &documentation_browser::historyChanged,
             this, &documentation::update_history_menus);

    // Init prev/next menus
    for (int i = 0; i < max_history_entries; ++i)
      {
        m_prev_pages_actions[i] = new QAction (this);
        m_prev_pages_actions[i]->setVisible (false);
        m_next_pages_actions[i] = new QAction (this);
        m_next_pages_actions[i]->setVisible (false);
        m_prev_pages_menu->addAction (m_prev_pages_actions[i]);
        m_next_pages_menu->addAction (m_next_pages_actions[i]);
      }

    connect (m_prev_pages_menu, &QMenu::triggered,
             this, &documentation::open_hist_url);
    connect (m_next_pages_menu, &QMenu::triggered,
             this, &documentation::open_hist_url);

    // Find
    m_tool_bar->addSeparator ();
    m_action_find
      = add_action (rmgr.icon ("edit-find"), tr ("Find"),
                    SLOT (activate_find (void)), this, m_tool_bar);

    // Zoom
    m_tool_bar->addSeparator ();
    m_action_zoom_in
      = add_action (rmgr.icon ("zoom-in"), tr ("Zoom in"),
                    SLOT (zoom_in (void)), m_doc_browser, m_tool_bar);
    m_action_zoom_out
      = add_action (rmgr.icon ("zoom-out"), tr ("Zoom out"),
                    SLOT (zoom_out (void)), m_doc_browser, m_tool_bar);
    m_action_zoom_original
      = add_action (rmgr.icon ("zoom-original"), tr ("Zoom original"),
                    SLOT (zoom_original (void)), m_doc_browser, m_tool_bar);

    // Bookmarks (connect slots later)
    m_tool_bar->addSeparator ();
    m_action_bookmark
      = add_action (rmgr.icon ("bookmark-new"), tr ("Bookmark current page"),
                    nullptr, nullptr, m_tool_bar);
  }

  void documentation::global_search (void)
  {
    if (! m_help_engine)
      return;

    QString query_string;
#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
    QString queries
      = m_help_engine->searchEngine ()->queryWidget ()->searchInput ();
    query_string = queries;
#else
    // FIXME: drop this part when support for Qt4 is dropped
    QList<QHelpSearchQuery> queries
      = m_help_engine->searchEngine ()->queryWidget ()->query ();
    if (queries.count ())
      query_string = queries.first ().wordList.join (" ");
    else
      query_string = "";
#endif

    if (query_string.isEmpty ())
      return;

    // Get quoted search strings first, then take first string as fall back
    QRegExp rx ("\"([^\"]*)\"");
    if (rx.indexIn (query_string, 0) != -1)
      m_internal_search = rx.cap (1);
    else
#if defined (HAVE_QT_SPLITBEHAVIOR_ENUM)
      m_internal_search = query_string.split (" ", Qt::SkipEmptyParts).first ();
#else
      m_internal_search = query_string.split (" ", QString::SkipEmptyParts).first ();
#endif

    m_help_engine->searchEngine ()->search (queries);
  }

  void documentation::global_search_started (void)
  {
    qApp->setOverrideCursor(QCursor(Qt::WaitCursor));
  }

  void documentation::global_search_finished (int)
  {
    if (! m_help_engine)
      return;

    if (! m_internal_search.isEmpty ())
      {
        m_query_string = m_internal_search;

        QHelpSearchEngine *search_engine = m_help_engine->searchEngine ();
        if (search_engine)
          {
#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
            QVector<QHelpSearchResult> res
              = search_engine->searchResults (0, search_engine->searchResultCount ());
#else
            QList< QPair<QString, QString> > res
              = search_engine->hits (0, search_engine->hitCount ());
#endif

            if (res.count ())
              {
                QUrl url;

                if (res.count () == 1)
#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
                  url = res.front ().url ();
#else
                  url = res.front ().first;
#endif
                else
                  {
                    // Remove the quotes we added
                    QString search_string = m_internal_search;

                    for (auto r = res.begin (); r != res.end (); r++)
                      {
#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
                        QString title = r->title ().toLower ();
                        QUrl tmpurl = r->url ();
#else
                        QString title = r->second.toLower ();
                        QUrl tmpurl = r->first;
#endif
                        if (title.contains (search_string.toLower ()))
                          {
                            if (title.indexOf (search_string.toLower ()) == 0)
                              {
                                url = tmpurl;
                                break;
                              }
                            else if (url.isEmpty ())
                              url = tmpurl;
                          }
                      }
                  }

                if (! url.isEmpty ())
                  {
                    connect (this, &documentation::show_single_result,
                             this, &documentation::handle_search_result_clicked);

                    emit show_single_result (url);
                  }
              }
          }

        m_internal_search = QString ();
      }

    qApp->restoreOverrideCursor();
  }

  void documentation::handle_search_result_clicked (const QUrl& url)
  {
    // Open url with matching text
    m_doc_browser->handle_index_clicked (url);

    // Select all occurrences of matching text
    select_all_occurrences (m_query_string);

    // Open search widget with matching text as search string
    m_find_line_edit->setText (m_query_string);
    m_find_line_edit->parentWidget ()->show ();

    // If no occurrence can be found go to the top of the page
    if (! m_doc_browser->find (m_find_line_edit->text ()))
      m_doc_browser->moveCursor (QTextCursor::Start);
    else
      {
        // Go to to first occurrence of search text.  Going to the end and then
        // search backwards until the last occurrence ensures the search text
        // is visible in the first line of the visible part of the text.
        m_doc_browser->moveCursor (QTextCursor::End);
        while (m_doc_browser->find (m_find_line_edit->text (),
                                    QTextDocument::FindBackward));
      }
  }

  void documentation::select_all_occurrences (const QString& text)
  {
    // Get highlight background and text color
    QPalette pal = QApplication::palette ();
    QTextCharFormat format;
    QColor col = pal.color (QPalette::Highlight);
    col.setAlphaF (0.25);
    format.setBackground (QBrush (col));
    format.setForeground (QBrush (pal.color (QPalette::Text)));

    // Create list for extra selected items
    QList<QTextEdit::ExtraSelection> selected;
    m_doc_browser->moveCursor (QTextCursor::Start);

    // Find all occurrences and add them to the selection
    while ( m_doc_browser->find (text) )
      {
        QTextEdit::ExtraSelection selected_item;
        selected_item.cursor = m_doc_browser->textCursor ();
        selected_item.format = format;
        selected.append (selected_item);
      }

    // Apply selection and move back to the beginning
    m_doc_browser->setExtraSelections (selected);
    m_doc_browser->moveCursor (QTextCursor::Start);
  }

  void documentation::notice_settings (const gui_settings *settings)
  {
    // If m_help_engine is not defined, the objects accessed by this method
    // are not valid.  Thus, just return in this case.
    if (! m_help_engine)
      return;

    // Icon size in the toolbar.
    int size_idx = settings->value (global_icon_size).toInt ();
    size_idx = (size_idx > 0) - (size_idx < 0) + 1;  // Make valid index from 0 to 2

    QStyle *st = style ();
    int icon_size = st->pixelMetric (global_icon_sizes[size_idx]);
    m_tool_bar->setIconSize (QSize (icon_size, icon_size));

    // Shortcuts
    shortcut_manager& scmgr = m_octave_qobj.get_shortcut_manager ();

    scmgr.set_shortcut (m_action_find, sc_edit_edit_find_replace);
    scmgr.shortcut (m_findnext_shortcut, sc_edit_edit_find_next);
    scmgr.shortcut (m_findprev_shortcut, sc_edit_edit_find_previous);
    scmgr.set_shortcut (m_action_zoom_in, sc_edit_view_zoom_in);
    scmgr.set_shortcut (m_action_zoom_out, sc_edit_view_zoom_out);
    scmgr.set_shortcut (m_action_zoom_original, sc_edit_view_zoom_normal);
    scmgr.set_shortcut (m_action_go_home, sc_doc_go_home);
    scmgr.set_shortcut (m_action_go_prev, sc_doc_go_back);
    scmgr.set_shortcut (m_action_go_next, sc_doc_go_next);
    scmgr.set_shortcut (m_action_bookmark, sc_doc_bookmark);

    // Settings for the browser
    m_doc_browser->notice_settings (settings);
  }

  void documentation::save_settings (void)
  {
    resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
    gui_settings *settings = rmgr.get_settings ();

    m_doc_browser->save_settings (settings);
    m_bookmarks->save_settings (settings);
  }

  void documentation::copyClipboard (void)
  {
    if (m_doc_browser->hasFocus ())
      {
        m_doc_browser->copy();
      }
  }

  void documentation::pasteClipboard (void) { }

  void documentation::selectAll (void) { }

  void documentation::load_index (void)
  {
    m_indexed = true;

    // Show index if no other page is required.
    if (m_current_ref_name.isEmpty ())
      m_doc_browser->setSource
        (QUrl ("qthelp://org.octave.interpreter-1.0/doc/octave.html/index.html"));
    else
      load_ref (m_current_ref_name);

    m_help_engine->contentWidget ()->expandToDepth (0);
  }

  void documentation::load_ref (const QString& ref_name)
  {
    if (! m_help_engine || ref_name.isEmpty ())
      return;

    m_current_ref_name = ref_name;

    if (! m_indexed)
      return;

#if defined (HAVE_QHELPENGINE_DOCUMENTSFORIDENTIFIER)
    QList<QHelpLink> found_links
      = m_help_engine->documentsForIdentifier (ref_name);
#else
    QMap<QString, QUrl> found_links
      = m_help_engine->linksForIdentifier (ref_name);
#endif

    QTabWidget *navi = static_cast<QTabWidget*> (widget (0));

    if (found_links.count() > 0)
      {
        // First search in the function index
#if defined (HAVE_QHELPENGINE_DOCUMENTSFORIDENTIFIER)
        QUrl first_url = found_links.constFirst().url;
#else
        QUrl first_url = found_links.constBegin().value ();
#endif

        m_doc_browser->setSource (first_url);

        // Switch to function index tab
        m_help_engine->indexWidget()->filterIndices (ref_name);
        QWidget *index_tab
          = navi->findChild<QWidget*> ("documentation_tab_index");
        navi->setCurrentWidget (index_tab);
      }
    else
      {
        // Use full text search to provide the best match
        QHelpSearchEngine *search_engine = m_help_engine->searchEngine ();
        QHelpSearchQueryWidget *search_query = search_engine->queryWidget ();

#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
        QString query = ref_name;
        query.prepend ("\"").append ("\"");
#else
        QList<QHelpSearchQuery> query;
        query << QHelpSearchQuery (QHelpSearchQuery::DEFAULT,
                                   QStringList (QString("\"") + ref_name + QString("\"")));
#endif
        m_internal_search = ref_name;
        search_engine->search (query);

        // Switch to search tab
#if defined (HAVE_QHELPSEARCHQUERYWIDGET_SEARCHINPUT)
        search_query->setSearchInput (query);
#else
        search_query->setQuery (query);
#endif
        QWidget *search_tab
          = navi->findChild<QWidget*> ("documentation_tab_search");
        navi->setCurrentWidget (search_tab);
      }
  }

  void documentation::activate_find (void)
  {
    if (m_find_line_edit->parentWidget ()->isVisible ())
      {
        m_find_line_edit->parentWidget ()->hide ();
        m_doc_browser->setFocus ();
      }
    else
      {
        m_find_line_edit->parentWidget ()->show ();
        m_find_line_edit->selectAll ();
        m_find_line_edit->setFocus ();
      }
  }

  void documentation::filter_update (const QString& expression)
  {
    if (! m_help_engine)
      return;

    QString wildcard;
    if (expression.contains (QLatin1Char('*')))
      wildcard = expression;

    m_help_engine->indexWidget ()->filterIndices(expression, wildcard);
  }

  void documentation::filter_update_history (void)
  {
    QString text = m_filter->currentText ();   // get current text
    int index = m_filter->findText (text);     // and its actual index

    if (index > -1)
      m_filter->removeItem (index);            // remove if already existing

    m_filter->insertItem (0, text);            // (re)insert at beginning
    m_filter->setCurrentIndex (0);
  }

  void documentation::find_backward (void)
  {
    find (true);
  }

  void documentation::find (bool backward)
  {
    if (! m_help_engine)
      return;

    QTextDocument::FindFlags find_flags;
    if (backward)
      find_flags = QTextDocument::FindBackward;

    if (! m_doc_browser->find (m_find_line_edit->text (), find_flags))
      {
        // Nothing was found, restart search from the begin or end of text
        QTextCursor textcur = m_doc_browser->textCursor ();
        if (backward)
          textcur.movePosition (QTextCursor::End);
        else
          textcur.movePosition (QTextCursor::Start);
        m_doc_browser->setTextCursor (textcur);
        m_doc_browser->find (m_find_line_edit->text (), find_flags);
      }

    record_anchor_position ();
  }

  void documentation::find_forward_from_anchor (const QString& text)
  {
    if (! m_help_engine)
      return;

    // Search from the current position
    QTextCursor textcur = m_doc_browser->textCursor ();
    textcur.setPosition (m_search_anchor_position);
    m_doc_browser->setTextCursor (textcur);

    if (! m_doc_browser->find (text))
      {
        // Nothing was found, restart search from the beginning
        textcur.movePosition (QTextCursor::Start);
        m_doc_browser->setTextCursor (textcur);
        m_doc_browser->find (text);
      }
  }

  void documentation::record_anchor_position (void)
  {
    if (! m_help_engine)
      return;

    m_search_anchor_position = m_doc_browser->textCursor ().position ();
  }

  void documentation::handle_cursor_position_change (void)
  {
    if (! m_help_engine)
      return;

    if (m_doc_browser->hasFocus ())
      record_anchor_position ();
  }

  void documentation::registerDoc (const QString& qch)
  {
    if (m_help_engine)
      {
        QString ns = m_help_engine->namespaceName (qch);
        bool do_setup = true;
        if (m_help_engine->registeredDocumentations ().contains (ns))
          {
            if (m_help_engine->documentationFileName (ns) == qch)
              do_setup = false;
            else
              {
                m_help_engine->unregisterDocumentation (ns);
                m_help_engine->registerDocumentation (qch);
              }
          }
        else if (! m_help_engine->registerDocumentation (qch))
          {
            QMessageBox::warning (this, tr ("Octave Documentation"),
                                  tr ("Unable to register help file %1.").
                                  arg (qch));
            return;
          }

        if (do_setup)
          m_help_engine->setupData();
      }
  }

  void documentation::unregisterDoc (const QString& qch)
  {
    if (! m_help_engine)
      return;

    QString ns = m_help_engine->namespaceName (qch);
    if (m_help_engine
        && m_help_engine->registeredDocumentations ().contains (ns)
        && m_help_engine->documentationFileName (ns) == qch)
      {
        m_help_engine->unregisterDocumentation (ns);
        m_help_engine->setupData ();
      }
  }

  void documentation::update_history_menus (void)
  {
    if (m_prev_pages_count != m_doc_browser->backwardHistoryCount ())
      {
        update_history (m_doc_browser->backwardHistoryCount (),
                        m_prev_pages_actions);
        m_prev_pages_count = m_doc_browser->backwardHistoryCount ();
      }

    if (m_next_pages_count != m_doc_browser->forwardHistoryCount ())
      {
        update_history (m_doc_browser->forwardHistoryCount (),
                        m_next_pages_actions);
        m_next_pages_count = m_doc_browser->forwardHistoryCount ();
      }
  }

  void documentation::update_history (int new_count, QAction **actions)
  {
    // Which menu has to be updated?
    int prev_next = -1;
    QAction *a = m_action_go_prev;
    if (actions == m_next_pages_actions)
      {
        prev_next = 1;
        a = m_action_go_next;
      }

    // Get maximal count limited by array size
    int count = qMin (new_count, int (max_history_entries));

    // Fill used menu entries
    for (int i = 0; i < count; i++)
      {
        QString title
          = title_and_anchor (m_doc_browser->historyTitle (prev_next*(i+1)),
                              m_doc_browser->historyUrl (prev_next*(i+1)));

        if (i == 0)
          a->setText (title); // set tool tip for prev/next buttons

        actions[i]->setText (title);
        actions[i]->setData (m_doc_browser->historyUrl (prev_next*(i+1)));
        actions[i]->setEnabled (true);
        actions[i]->setVisible (true);
      }

    // Hide unused menu entries
    for (int j = count; j < max_history_entries; j++)
      {
        actions[j]->setEnabled (false);
        actions[j]->setVisible (false);
      }
  }

  void documentation::open_hist_url (QAction *a)
  {
    m_doc_browser->setSource (a->data ().toUrl ());
  }

  // Utility functions

  QString documentation::title_and_anchor (const QString& title, const QUrl& url)
  {
    QString retval = title;
    QString u = url.toString ();

    retval.remove (QRegExp ("\\s*\\(*GNU Octave \\(version [^\\)]*\\)[: \\)]*"));

    // Since the title only contains the section name and not the
    // specific anchor, extract the latter from the url and append
    // it to the title
    if (u.contains ('#'))
      {
        // Get the anchor from the url
        QString anchor = u.split ('#').last ();
        // Remove internal string parts
        anchor.remove (QRegExp ("^index-"));
        anchor.remove (QRegExp ("^SEC_"));
        anchor.remove (QRegExp ("^XREF"));
        anchor.remove ("Concept-Index_cp_letter-");
        anchor.replace ("-"," ");

        // replace encoded special chars by their unencoded versions
        QRegExp rx = QRegExp ("_00([0-7][0-9a-f])");
        int pos = 0;
        while ((pos = rx.indexIn(anchor, pos)) != -1)
          {
            anchor.replace ("_00"+rx.cap (1), QChar (rx.cap (1).toInt (nullptr,16)));
            pos += rx.matchedLength();
          }

        if (retval != anchor)
          retval = retval + ": " + anchor;
      }

    return retval;
  }



  //
  // The documentation browser
  //

  documentation_browser::documentation_browser (QHelpEngine *he, QWidget *p)
    : QTextBrowser (p), m_help_engine (he), m_zoom_level (max_zoom_level+1)
  {
    setOpenLinks (false);
    connect (this, &documentation_browser::anchorClicked,
             this, [=] (const QUrl& url) { handle_index_clicked (url); });
  }

  void documentation_browser::handle_index_clicked (const QUrl& url,
                                                    const QString&)
  {
    if (url.scheme () == "qthelp")
      setSource (url);
    else
      QDesktopServices::openUrl (url);
  }

  void documentation_browser::notice_settings (const gui_settings *settings)
  {
    // Zoom level only at startup, not when other settings have changed
    if (m_zoom_level > max_zoom_level)
      {
        m_zoom_level = settings->value (dc_browser_zoom_level).toInt ();
        zoomIn (m_zoom_level);
      }
  }

  QVariant documentation_browser::loadResource (int type, const QUrl &url)
  {
    if (m_help_engine && url.scheme () == "qthelp")
      return QVariant (m_help_engine->fileData(url));
    else
      return QTextBrowser::loadResource(type, url);
  }

  void documentation_browser::save_settings (gui_settings *settings)
  {
    settings->setValue (dc_browser_zoom_level.key, m_zoom_level);

    settings->sync ();
  }

  void documentation_browser::zoom_in (void)
  {
    if (m_zoom_level < max_zoom_level)
      {
        zoomIn ();
        m_zoom_level++;
      }
  }

  void documentation_browser::zoom_out (void)
  {
    if (m_zoom_level > min_zoom_level)
      {
        zoomOut ();
        m_zoom_level--;
      }
  }

  void documentation_browser::zoom_original (void)
  {
    zoomIn (- m_zoom_level);
    m_zoom_level = 0;
  }

  void documentation_browser::wheelEvent (QWheelEvent *we)
  {
    if (we->modifiers () == Qt::ControlModifier)
      {
#if defined (HAVE_QWHEELEVENT_ANGLEDELTA)
        if (we->angleDelta().y () > 0)
#else
        if (we->delta() > 0)
#endif
          zoom_in ();
        else
          zoom_out ();

        we->accept ();
      }
    else
      QTextEdit::wheelEvent (we);
  }

}
